Currently, MPEG2 TS with a system clock frequency of 27 [MHz] is implemented in a media transport scheme of digital television broadcasting, and in the future, implementation of MMT (MPEG Media Transport) with a system clock frequency of 2N [Hz] is scheduled (for example, see NPL 1).
Therefore, both content corresponding to MPEG2 TS and content corresponding to MMT may be present in a period of transmission of the media transport scheme from MPEG2 TS to MMT, and a content reproduction apparatus that can receive and reproduce both types of content is necessary.
The system clock frequencies of MPEG2 TS and MMT are different as described above, and the content reproduction apparatus can be provided with two types of system clock lines having similar configurations, in which only the system clock frequencies are different.
FIG. 1 illustrates an example of a configuration of a content reproduction apparatus that can be conceived in the past, the content reproduction apparatus capable of receiving and reproducing both content corresponding to MPEG2 TS and content corresponding to MMT.
A content reproduction apparatus 10 mainly includes a content acquisition unit 11, an MMT processing unit 15, a TS processing unit 24, a selection unit 33, and a decoding unit 34.
The content acquisition unit 11 includes a communication unit 12, a reception unit 13, and a selection unit 14.
The communication unit 12 acquires a multiplexed stream corresponding to MMT or MPEG2 TS through a communication network 1 represented by the Internet and outputs the multiplexed stream to the selection unit 14. The reception unit 13 receives the multiplexed stream corresponding to MMT or MPEG2 TS through a broadcast network 2, such as a terrestrial broadcast network, a satellite broadcast network, and a CATV network, and outputs the multiplexed stream to the selection unit 14.
The selection unit 14 selects an output destination of the input multiplexed stream according to the media transport scheme of the multiplexed stream. Specifically, the selection unit 14 outputs the multiplexed stream corresponding to MMT to a demultiplexing unit 16 of the MMT processing unit 15 and outputs the multiplexed stream corresponding to MPEG2 TS to a demultiplexing unit 25 of the TS processing unit 24.
The MMT processing unit 15 belonging to the system clock line of MMT includes the demultiplexing unit 16, a clock recovery unit 17, a clock signal generation unit 22, and a Host I/F unit 23.
The demultiplexing unit 16 separates encoded data of the content from the multiplexed stream data corresponding to MMT and outputs the encoded data to the Host I/F unit 23. The demultiplexing unit 16 also separates a PSI (Program Specific Information) equivalent, a reference time information NTP (Network Time Protocol), and a presentation time information PTS (Presentation Time Stamp) from the multiplexed stream data corresponding to MMT and outputs them to the clock recovery unit 17.
The clock recovery unit 17 includes a clock generation unit 18, an NTP equivalent counting unit 19, a count comparison unit 20, and a clock control unit 21.
On the basis of a difference between the reference time information NTP input from the demultiplexing unit 16 and an NTP equivalent count value generated in the clock recovery unit 17, the clock recovery unit 17 controls the clock generation unit 18 that generates a system clock of 2N [Hz]. The clock recovery unit 17 recovers a system clock on the transmission side of the content (synchronizes with the system clock on the transmission side of the content) and outputs the recovered system clock to the clock signal generation unit 22.
The count comparison unit 20 of the clock recovery unit 17 sets, as Time Stamp Info, the reference time information NTP and the presentation time information PTS input from the demultiplexing unit 16 and outputs the Time Stamp Info to the Host I/F unit 23.
The clock signal generation unit 22 generates a baseband clock signal necessary for decoding the encoded data of MMT on the basis of the recovered system clock of 2N [Hz] and outputs the baseband clock signal to the selection unit 33. The Host I/F unit 23 outputs the encoded data, the reference time information NTP, and the presentation time information PTS input from the earlier stage to the selection unit 33.
Meanwhile, the TS processing unit 24 belonging to the system clock line of MPEG2 TS also has a configuration similar to the MMT processing unit 15. More specifically, the TS processing unit 24 includes the demultiplexing unit 25, a clock recovery unit 26, a clock signal generation unit 31, and a Host I/F unit 32.
The demultiplexing unit 25 separates encoded data of the content from the multiplexed stream data corresponding to MPEG2 TS and outputs the encoded data to the Host I/F unit 32. The demultiplexing unit 25 also separates PSI, a reference time information PCR (Program Clock Reference), and a presentation time information PTS from the multiplexed stream data corresponding to MPEG2 TS and outputs them to the clock recovery unit 26.
The clock recovery unit 26 includes a clock generation unit 27, an STC counting unit 28, a count comparison unit 29, and a clock control unit 30.
On the basis of a difference between the reference time information PCR and the presentation time information PTS input from the demultiplexing unit 25 as well as an STC (System Time Clock) count value generated in the clock recovery unit 17, the clock recovery unit 26 controls the clock generation unit 27 that generates a system clock of 27 [MHz]. The clock recovery unit 26 recovers the system clock on the transmission side of the content (synchronizes with the system clock on the transmission side of the content) and outputs the recovered system clock to the clock signal generation unit 31.
The count comparison unit 29 of the clock recovery unit 26 sets, as Time Stamp Info, the reference time information PCR and the presentation time information PTS input from the demultiplexing unit 25 and outputs the Time Stamp Info to the Host I/F unit 32.
The clock signal generation unit 31 generates a baseband clock signal necessary for decoding the encoded data of MPEG2 TS on the basis of the recovered system clock of 27 [MHz] and outputs the baseband clock signal to the selection unit 33. The Host I/F unit 32 outputs the encoded data, the reference time information PCR, and the presentation time information PTS input from the earlier stage to the selection unit 33.
The selection unit 33 outputs, to the decoding unit 34, a set of the baseband clock signal, the encoded data, the reference time information NTP, and the presentation time information PTS synchronized with the system clock of 2N [Hz] input from the MMT processing unit 15 or a set of the baseband clock signal, the encoded data, the reference time information PCR, and the presentation time information PTS synchronized with the system clock of 27 [MHz] input from the TS processing unit 24.
The decoding unit 34 decodes the encoded data according to the baseband clock signal input from the MMT processing unit 15 through the selection unit 33. The decoding unit 34 synchronizes a video signal and an audio signal obtained as a result of the decoding on the basis of the presentation time information PTS and outputs the video signal and the audio signal to the later stage. The decoding unit 34 also decodes the encoded data encoded data according to the baseband clock signal input from the TS processing unit 24 through the selection unit 33. The decoding unit 34 synchronizes a video signal and an audio signal obtained as a result of the decoding on the basis of the presentation time information PTS and outputs the video signal and the audio signal to the later stage.